West Nile virus is a potentially serious illness that is most often spread through the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the virus to humans and other animals. West Nile virus has been detected in all lower 48 states (but not in Hawaii or Alaska) and outbreaks of disease have been occurring in the United States every summer since 1999.

The first human cases of West Nile virus in Clark County, along with the first positive mosquitoes, were reported in 2004. The health district conducts surveillance of mosquito populations to monitor the level of virus throughout the valley. Every year since then (except 2010), the virus has been found in both humans and mosquitoes. West Nile virus is now endemic in Clark County, which means we expect to see the virus every year during the mosquito season, which occurs April through November.

The most effective way to avoid West Nile virus disease is to prevent mosquito bites. You can play an important role in monitoring West Nile virus by reporting stagnant water, green swimming pools or other potential mosquito breeding sources to your local code enforcement agency. Visit the Mosquito Surveillance for more information on reporting mosquito activity to the health district. For additional information on West Nile virus visit the Frequently Asked Questions page or the Nevada Department of Agriculture's website.